Downstems go hand in hand when it comes to smoking from a glass bong and even some dab rigs. Downstems are the heart of a glass bong, and they are essential in carrying the  the smoke from your bowl piece to your mouth. Downstems come in a variety of sizes, styles and have many style percs to chose from. Some of the most popular perc styles are showerhead, slitted, multi hole and gridded, each function a little differently than the other. Before ordering your next downstem, make sure to measure the length of the downstem needed by measuring from the top of the joint to the end of the downstem. Typically downstems come in 14mm, 18mm and also 14/18mm downstems which are great for using your 14mm bowl in an 18mm bong or rig joint.